1. Field of the Invention
The present invention relates to a controller and control method for an optical storage drive. More particularly, the present invention relates to a controller having a non-volatile memory stored with information for management of an optical storage drive and also pertains to an optical storage drive control method using such a non-volatile memory.
In a typical optical disk drive (including magneto-optical disk drive), illuminating light from a laser diode in an optical head is applied to the surface of a rotating disk-shaped recording medium, i.e., optical disk, thereby recording information. The recorded information is reproduced by detecting changes in properties (quantity of light, plane of polarization, etc.) of the reflected light from the optical disk, which is illuminated with the light from the optical head. The optical disk has information tracks provided over the surface thereof from the inner periphery to the outer periphery of the disk. Since there are differences in operating characteristics among optical disk drives, management information such as control information differs for each drive. For this reason, a memory for storing management information for each individual drive is needed.
2. Description of the Related Art
Since optical disk drives that use a laser light source vary from each other in operating characteristics, it is necessary to give various considerations as follows.
Firstly, an optical disk drive needs to output a predetermined level of light power from a laser light source. Therefore, before the drive is started to operate, for example, when the power supply is turned on, the drive current for the laser light source is adjusted so that the output of the laser light source coincides with a predetermined level of light power. This process is termed emission adjustment. However, laser light sources, particularly laser diodes, degrade when used for a long time or if an overcurrent is applied thereto. If the laser light source degrades, the value of the drive current required for outputting a predetermined level of light power increases. If the degradation further progresses, it becomes impossible to obtain the required light power even if the maximum current is supplied. In such a case, recording, reproduction, etc. cannot normally be effected any longer.
Accordingly, it is necessary to check the lifetime of the laser diode of the optical head beforehand. For this purpose, the following method has heretofore been employed: A limit current value obtained from design values is preset, and upon completion of the emission adjustment, the current value obtained by the emission adjustment is compared with the limit current value. If the adjusted current value exceeds the limit current value, it is decided that the lifetime of the laser diode has expired.
With this method, however, it is difficult to set the limit current value uniquely because of variation in circuit and laser light source performances among optical disk drives. In addition, if the limit current value is set at a large value, some laser light sources may become degraded before the adjusted current value reaches the limit current value, resulting in a failure to effect a normal write/read operation. If the limit current value is set at a small value, it may be decided that the lifetime of the laser light source has expired before it becomes completely degraded. In such a case, the laser light source is replaced with a new one although it is still usable, which is wasteful.
Secondly, when data is to be written with an optical disk drive, if the write power and the write pulse width deviate from the optimum values, a proper write operation cannot be effected. In general, after a write operation, data written is read (termed "verify read") to check whether or not the data has normally been written. In this way, the write operation can be confirmed. Even if the write operation has not properly been effected, write data errors can be relieved to a certain extent by ECC (Error Correcting Code) processing of the reproduced signal.
However, if the number of data errors increases, it may become impossible to correct all the data errors even by ECC processing. In such a case, the written data is rewritten to an alternate region (alternate block) provided in a certain area on the optical disk medium, thereby relieving the error. This is termed alternate processing. Accordingly, if the write power and the write pulse width deviate from the optimum values, there will be an increase in the number of times when it is decided by the verify read that the data has not normally been written and hence the alternate processing is executed.
Since the number of alternate blocks is limited, if the alternate processing is executed many times, the alternate blocks may be used up. In such a case, it becomes impossible to write data to the medium any longer although the area of the medium used for normal recording has not yet been used up, which is extremely wasteful.
Further, if the write power and the write pulse width deviate from the optimum values at the time of writing, data may be written to the very limit of the margin even if it is decided by the verify read that the data has normally been written. For this reason, degradiation of the medium by aging and the number of stains on the medium surface increases, the incidence of data read errors increases in comparison to the incidence of data errors at the time of writing. Accordingly, it may be impossible to correct all the data errors even by the ECC processing. This gives rise to a problem that data which must have normally been written cannot be read afterward.
Hitherto, optimum values for write conditions have been uniquely determined for all drives by experiments and set in firmware as parameters during design or manufacture. However, there is variation in performance of circuits and optical systems among optical disk drives, and optimum write values differ for each drive. Accordingly, in each individual optical disk drive, the uniquely set write conditions may deviate from the actual optimum values, so that the drive cannot exhibit the given write performance. It may be considered to adopt a method wherein optimum write values are measured for each individual optical disk drive and the measured values are set by using DIP switches, for example. With this method, however, the operation is difficult to automate and hence complicated.
Thirdly, optical disk drives are widely used, and many optical disk drives appear in the field. These drives vary from each other in the performance of the optical head and that of the seek mechanism, although such performance variation is within a certain range. Therefore, it is common practice to operate each individual optical disk drive at the time of startup before shipment to check the operating performance of the drive. Further, at the time of extra maintenance (replacement or adjustment of a unit due to occurrence of a fault) or regular maintenance after the shipment, the optical disk drive is operated to make a diagnosis on the operating performance. For example, a magneto-optical disk drive is operated and measured for the CNR (Carrier-to-Noise Ratio) of the reproduced signal, the write/read error rate and the average seek speed by using a tester, thereby making a diagnosis on the operating performance. For such drives as vary in performance from each other, it is necessary to manage data on the performance of each individual drive in order to verify the performance.
In the conventional management of the optical disk drive performance, data on the operating performance, which is measured at the time of startup before shipment, is recorded on a data sheet for each drive, and this data sheet is kept for maintenance purposes. At the time of replacement or adjustment of a unit or during regular maintenance after the shipment, the optical disk drive is operated to measure the operating performance. If the measured values are within a predetermined normal range, the operating performance is judged to be good, and the results of the measurement are recorded on a data sheet, e.g., a maintenance table. In this way, data on the operating performance of each individual optical disk drive has heretofore been managed.
Although the operating performance measured at the time of startup before shipment is the reference performance of the optical disk drive, the actual operating performance cannot be checked by comparison with it. Therefore, at the time of replacement of a unit, for example, it is impossible to check accurately whether or not the required performance is satisfactorily obtained with the new unit. Thus, the checking can be made only approximately. It may be considered to utilize the data sheet, prepared for the optical disk drive concerned at the time of startup before shipment, when a unit is replaced or adjusted. However, it is not easy to manage data sheets for optical disk drives which are shipped in large quantities abroad as well as at home. It is practically impossible to find the associated data sheet when a fault has occurred.